This invention relates to a photoconductor drum having a hollow cylindrical base element with a coating on the outer surface including at least one photosensitive layer, the base element concentrically accommodating at least one core element which is made at least partially cylindrical and which is made at least partially of plastic.
A photoconductor drum of the initially mentioned type is described for example in EP 0 526 208 A1. Photoconductor drums of this type are used for example in copiers or printers. The photosensitive layer on the outer surface of the photoconductor drum is electrically charged or discharged by being brought into contact with an electrically conductive roller which rolls on the circumference of the photoconductor drum. This roller which is used for charging and discharging transmits a dc voltage with a relatively high frequency to the photoconductor drum. By this continuous charging and discharging process the photoconductor drum and the charging roller are alternately attracted and repelled. The resulting vibrations produce noise which is undesirable. EP 0 526 208 A1 proposes various measures for noise suppression, these suppression measures being mainly electronic. It is also mentioned in the embodiments that the photoconductor drum can consist of a hollow, cylindrical base element which accommodates a core element which is made roughly cylindrical and which consists at least partially of plastic.
The object of this invention is to devise a photoconductor drum with improved properties with respect to damping of noise development in the charging and discharging process which far surpasses the existing art.
Achieving this object there is disclosed a photoconductor drum of made of a hollow cylindrical base element with a coating on the outer surface thereof. There is a core element made partially of plastic which has on its outer surface which comes into contact with the inside of the base element various irregularities or roughness. It was ascertained that this design leads to better noise damping, since the vibrations are damped during the mutual alternating attraction and repulsion between the photoconductor drum and the charging roller. The vibration behavior of the photoconductor drum is especially improved by the core element which is made at least partially of plastic. It is no longer in contact, over its entire surface, with the generally metal base element in the initial state, but only in the area of the irregularities which project to the outside on the outer surface of the core element.
According to one development of the invention, the vibration behavior is further improved when the core element is made entirely of plastic. This enables simplified production of the core element, which can be, for example, an injection molded part.
These irregularities of the outer surface of the core element can be formed, for example, by nubs or knurling of the surface. This knurling can take place by mechanical working of the surface of the core element which can follow the production process, for example, by injection molding. The core element can equally well be injected beforehand in a corresponding mold with irregularities on the outer surface, for example, with nubs. These nubs can be for example roughly annular. Within these annular nubs there can be cylindrical and/or conical crater-like depressions, so that elevations relative to the actual outer surface of the core element and moreover, depressions are formed. One sample version of the invention calls for nub-like elevations to be located in the same areas as the crater-like depressions, for example, the nub-like annular elevations surrounding the crater-like depressions.
The core element need not be solid, but can be hollow inside. For example, the core element, within the framework of the invention, can have a cylindrical, or conical, inner cavity so that it is made in principle, annular, the material being saved and vibration-damping properties being good.
The core elemen, which due to the vibration-damping properties, can also be called an equalizer, and can be made for example of plastics, such as polypropylene, polyethylene, polyamide, or the like. Mixtures of these materials, or other plastics, are also possible. The core element can be made of a uniform material, or of several components. After production, for example, roughness of the surface can be achieved by roughening with a knurling tool. Then, preferably, the core element (equalizer) is pressed into the generally cylindrical metal base element of the photoconductor drum. This pressing can take place such that the equalizer locks and no additional mounting means are necessary. The base element of the photoconductor drum can be made, for example, of an aluminum tube with an outer photosensitive coating. The weight of the plastic core element can be, for example, in the range between roughly 40 and roughly 150 g and is preferably in the range between roughly 50 and 70 g. For a weight in these ranges especially good vibration-damping properties can be established.
The core element can have a rough annular molded attachment (cone gate) on at least one end side. Cone gates provided on the equalizer are advantageous on both sides in order to achieve better filling behavior in the tool during injection molding. They have no function for the actual damping in the image carrier.